Title: The lost p1 allele in sh2 sweet corn: Quantitative effects of p1 and a1 genes on the concentrations of maysin, apimaysin, methoxymaysin, and chlorogenic acid in maize silk, and the antibiotic activity against corn earworm

Technical Abstract:
The flavor of sh2 super-sweet corn is preferred by consumers. Unfortunately, sh2 sweet corn has very little genetic variation for resistance to insects. This presentation will review and summarize the studies of the functions of two loci, p1 and a1. The P1 allele can have a major role in the resistance of sh2 sweet corn to corn earworm, an allele that was lost in the historical development of sweet corn because of its pleiotropic effect on the undesirable cob color and silk browning. The P1 allele has significant effects on biosyntheses of silk antibiotic compounds, maysin, apimaysin, methoxymaysin, and chlorogenic acid. Therefore, improvement of chlorogenic acid and AM-maysin (apimaysin and 3’-methoxymaysin) may be important to the capacity of host plants’ resistance to insects when individuals have substantial amount of these minor compounds. The effect of a1 gene shows dominant gene action for low maysin and significant epistatic gene action with p1gene. The dominant functional allele A1 causes anthocyanin pigments to form in the aleurone, plant, and pericarp tissues, the recessive nonfunctional a1 allele causes absence of pigment (colorless) in these tissues. The presence of maysin and its analogues with antibiotic activity in silks is an important defense against invasion of the ear by corn earworm. A thorough knowledge of the inheritance of these compounds will assist breeders in choosing the most efficient method of incorporating this trait into elite sweet corn inbred lines. Silk maysin concentrations above 0.2% begin to substantially reduce larval growth and prevent completion of the life cycle when husk coverage is sufficient to force the insect to feed on silks while entering the ear. If silk browning and cob color are critical factors for maysin production in sweet corn but lacks customer’s preference, then separating the red cob and browning silk, which are controlled by the P1 allele, may be difficult, if not impossible. There are some field corn germplasm with p1-wwr alleles (clear pericarp, white cob, browning silks), but the amount of antibiotic flavones and their potential as a donor need further investigation.